Are immigrants outbred and unrelated? Testing standard assumptions in a wild metapopulation

Abstract

Immigration into small recipient populations is expected to alleviate inbreeding and increase genetic variation, and hence facilitate population persistence through genetic and/or evolutionary rescue. Such expectations depend on three standard assumptions: that immigrants are outbred, unrelated to existing natives at arrival, and unrelated to each other. These assumptions are rarely explicitly verified, including in key field systems in evolutionary ecology. Yet, they could be violated due to non-random or repeated immigration from adjacent small populations. We combined molecular genetic marker data for 150-160 microsatellite loci with comprehensive pedigree data to test the three assumptions for a song sparrow (Melospiza melodia) population that is a model system for quantifying effects of inbreeding and immigration in the wild. Immigrants were less homozygous than existing natives on average, with mean homozygosity that closely resembled outbred natives. Immigrants can therefore be considered outbred on the focal population scale. Comparisons of homozygosity of real or hypothetical offspring of immigrantnative, native-native and immigrant-immigrant pairings implied that immigrants were typically unrelated to existing natives and to each other. Indeed, immigrants' offspring would be even less homozygous than outbred individuals on the focal population scale. The three standard assumptions of population genetic and evolutionary theory were consequently largely validated. Yet, our analyses revealed some deviations that should be accounted for in future analyses of heterosis and inbreeding depression, implying that the three assumptions should be verified in other systems to probe patterns of non-random or repeated dispersal and facilitate precise and unbiased estimation of key evolutionary parameters.

Kinship and similarity drive coordination of breeding-group choice in male spotted hyenas

“…By showing that dispersal and breeding-group choice may often be coordinated, our findings contribute to the growing evidence [2,17,62] that coordinated breeding-group choice and dispersal is an overlooked driver in social evolution. Our study underscores the importance to account for kinship and similarity, in particular in origin, between dispersers in theoretical and empirical studies of animal movement and population genetics (see also [63]).…”

“…different choice same choice difference in date of clan choice (days) littermates (30) peers (63) strangers (55)…”

Inbreeding is associated with shorter early-life telomere length in a wild passerine

“…1e). This suggests that longer telomeres in outbred individuals may partly be attributed to a general heterosis effect (Charlesworth & Willis, 2009) involving mating between immigrants and native individuals (Dickel et al, 2021;Ebert et al, 2002). In our study metapopulation, the proportion of dispersers among recruits can be high among the island populations (0.2 on average ranging from 0.0-1.0 across years and islands, Ranke et al, 2021;Saatoglu et al, 2021), and hence most islands are not strongly differentiated (Niskanen et al, 2020).…”

Immune genotypes, immune responses, and survival in a wild bird population

“…Since 1993, all individuals have been genotyped at 13 highly polymorphic microsatellite loci, facilitating construction of a precise genetic pedigree from which lifetime reproductive success and f are estimated with high precision (Nietlisbach et al, 2015, 2017; Reid et al, 2021; Sardell et al, 2010). Immigrants to Mandarte (~1 per year on average) are assumed to be unrelated to existing residents, and their offspring are assigned f = 0 (Dickel et al, 2021; Germain et al, 2016; Wilson & Arcese, 2008). Emigration appears to be rare; an annual re‐sighting probability of ≥0.99 ensures that local survival is assessed precisely based on annual censuses conducted in late April (Wilson et al, 2007; Wilson & Arcese, 2008).…”

“…Since 1993, all individuals have been genotyped at 13 highly polymorphic microsatellite loci, facilitating construction of a precise genetic pedigree from which lifetime reproductive success and f are estimated with high precision (Nietlisbach et al, 2015(Nietlisbach et al, , 2017Reid et al, 2021;Sardell et al, 2010). Immigrants to Mandarte (~1 per year on average) are assumed to be unrelated to existing residents, and their offspring are assigned f = 0 (Dickel et al, 2021;Germain et al, 2016;Wilson & Arcese, 2008).…”